There have been various proposals on the method of producing isobutylene glycol. For example, Japanese Patent Application Laid-Open No. 53-12804 discloses a method of producing isobutylene chlorohydrin and isobutylene glycol by reacting isobutene with oxygen-containing gas in an aqueous solution containing halide ion in the presence of a compound or ion of an element selected from the group consisting of tin, tellurium, iridium and titanium. Japanese Patent Application Laid-Open No. 53-65807 discloses a liquid phase oxidation of isobutene in an aqueous solvent in the presence of a catalyst. Japanese Patent Application Laid-Open No. 58-144331 discloses a method of producing a vicinal glycol by irradiating methanol with light in the presence of acetone. Japanese Patent Application Laid-Open No. 59-95226discloses a method of producing diols by hydrogenation of acetone cyanohydrin in a water-containing medium, comprising a fist step of hydrogenating acetone cyanohydrin until one mol of hydrogen is absorbed per one mol of acetone cyanohydrin at -20 to 20.degree. C. under a hydrogen pressure of 10 bar or lower in the presence of a palladium or platinum catalyst and an acid in an amount equivalent to acetone cyanohydrin or more, or in the presence of metallic nickel and an acid in an amount equivalent to acetone cyanohydrin or more, and a second step of hydrogenating acetone cyanohydrin at 30 to 100.degree. C. under a hydrogen pressure of 10 to 150 bar in the presence of metallic nickel.
However, the above methods have problems in putting them into industrial application. For example, in the oxidation of isobutene with oxygen in the presence of hydrogen bromide and tellurium oxide catalyst described in Japanese Patent Application Laid-Open No. 53-12804, isobutylene chlorohydrin is produced 2.6 times as much as isobutylene glycol, thereby resulting in a disadvantageously low yield of isobutylene glycol. In the air oxidation of isobutylene in water solvent in the presence of potassium dichromate described in Japanese Patent Application Laid-Open No. 53-65807,the rate of reaction is low and the yield of isobutylene glycol is unfavorably as low as 38%. In the method taught by Japanese Patent Application Laid-Open No. 58-144331, methanol and acetone in a pyrex reactor are irradiated with light from a high pressure mercury lamp. This method has defects of low rate of reaction and low selectivity to isobutylene glycol due to by-production of ethylene glycol and pinacol. Although the method taught by Japanese Patent Application Laid-Open No. 59-95226 provides a yield of isobutylene glycol relatively as high as 81%, it requires rather complicated reaction operations for industrial use.